1. Field of the Invention
This invention relates generally to the load sensing controls of a load responsive system.
In more particular aspects this invention relates to positive and negative load pressure identifying and transmitting controls, for use in load responsive systems.
In still more particular aspects this invention relates to positive and negative load pressure identifying and transmitting controls, which can respond with direction control spool in its neutral position, in anticipation of the system demand.
2. Description of the Prior Art
Load pressure sensing, identifying and transmitting circuits are widely used in control of load responsive systems. Such load pressure sensing, identifying and transmitting circuits usually employ check valve or shuttle valve logic systems, in identification of maximum system load pressure, while various types of load pressure sensing ports, sequentially interconnected by the direction control spool, are used in identification of whether the load pressure signal is positive or negative.
The presence of such load sensing ports, positioned in the bore of a direction control spool, inevitably increases the total spool stroke and dead band of the spool, making the control less sensitive. In order not to increase the dead band of the valve, the flow area of the load pressure sensing ports is selected as small as possible, resulting in substantial attenuation of the signal and greatly affecting the response of the compensating controls. Such load pressure sensing ports are shown in my U.S. Pat No. 4,154,261, issued May 15, 1979. Since such load pressure sensing ports are gradually uncovered, with the displacement of the direction control spool from its neutral position, at small displacements the attenuation of the load pressure signal is very great. This type of load pressure sensing circuit suffers from one additional disadvantage. Since the movement of the direction control spool is directly used in interconnecting the load pressure signal to the compensator or pump controls, it is impossible to transmit such signals with the direction control spool in its neutral position and in anticipation of the control function. Such a load sensing circuit, provided with the feature of anticipation, is shown in my U.S. Pat. No. 4,610,194, issued Sept. 9, 1986. This type of load sensing circuit, although very effective, suffers from one disadvantage in that the load pressure signal identifying shuttle might be adversely affected with very rapid change in the control pressure differential of the spool position control signals.